The first of the guidelines is fairly self explanatory: your model should be devoid of any holes that would cause it not to be water-tight.
In regards to the second guideline, it essentially means that each water-tight mesh must be joined in a certain manner to have the overall object still water-tight. There are multiple tools to detect manifold violations prior to printing, and failure to have a manifold object can result in adverse results.
For example, with this object:
We see a manifold violation in the center edge connecting the two meshes, although each are perfectly valid.
This is a fundamental manifold violation and requires a serious change in the object in order to fix it.
A video containing the guidelines as to how 3D objects should be painted can be found here: Painting Guidelines.
Four main guidelines should be followed:
An example of sizes and minimum wall thickness can be found at Shapeways:
Guidelines for various materials.
The first of the guidelines is fairly self explanatory: your model should be devoid of any holes that would cause it not to be water-tight.
In regards to the second guideline, it essentially means that each water-tight mesh must be joined in a certain manner to have the overall object still water-tight. There are multiple tools to detect manifold violations prior to printing, and failure to have a manifold object can result in adverse results.
For example, with this object:
We see a manifold violation in the center edge connecting the two meshes, although each are perfectly valid.
This is a fundamental manifold violation and requires a serious change in the object in order to fix it.
A video containing the guidelines as to how 3D objects should be painted can be found here: Painting Guidelines.